Fine grain strengthening and toughening double-medium-step quenching cooling method for steel

Abstract

The invention discloses a fine grain strengthening and toughening double-medium-step quenching cooling method for steel. By applying the law of'martensite transformation reversibility ', fine grains are strengthened and toughened for many times by a heat treatment method. In the austenitizing process of the steel, conditions are provided for martensite reversion; after steel with martensite reversion conditions is austenitized, pre-cooled water cooling bypasses a C-curve unstable area to a martensite area and is not cooled thoroughly, martensite crystal nucleuses gradually grow up along with temperature reduction, temperature return and temperature rise of outlet water are achieved through waste heat, martensite synchronously shrinks along with temperature rise in turn, and in other words, fine grain strengthening and toughening are achieved. Comprising the following steps: austenitizing steel to provide conditions for martensite reversion; the steel is pre-cooled, so that the thermal stress is reduced; and steel controlled cooling is conducted, and water cooling-temperature returning is conducted for multiple times till the temperature is reduced to the room temperature. The method can save energy, protect the environment and strengthen fine grains, the tensile strength is improved to be greater than the yield strength, the yield ratio is reduced, and the problem of strengthening and toughening the fine grains at the 1 / 2T position of the large-section steel part is solved.

Description

technical field [0001] The invention relates to a heat treatment method for steel, in particular to a dual-medium-graded quenching and cooling method for fine-grain strengthening and toughening of steel. Background technique [0002] The fine-grain strengthening of the prior art steel has high energy and resource consumption, serious pollution, high cost, and the quality and technical indicators at 1 / 2T of large-section steel pieces are difficult to meet the standard; the prior art features are: [0003] The fine-grain strengthening of steel is to add in the steel: alloying elements that reduce the critical point, such as Mn, Cr, Mo, etc.; increase the nucleation rate, and prevent the growth of austenite grains in the hot state. Microalloying elements, such as Ti, Nb, V, etc.; the increase in yield strength is greater than the increase in tensile strength, and the increase in yield strength is restricted to not exceed 110% of the standard value, and the ratio of yield to str...

AI Technical Summary

Problems solved by technology

[0002] The fine-grain strengthening of steel in the prior art requires large energy and resource consumption, serious pollution, high cost, and the quality and technical indicators at 1 / 2T of large cross-section steel parts are difficult to meet the standard; the characteristics of the existing technology are:

Images